1. Field of the Invention
The present invention relates to an accommodation cassette for accommodating a frame unit having a wafer attached thereto via an attachment tape in an opening formed at the central portion of the frame unit or directly accommodating a wafer without a frame unit.
2. Description of the Related Art
As is known to those skilled in the art, an accommodation cassette is widely used to accommodate frame units each having a wafer attached thereto via an attachment tape in an opening formed at the central portion of the frame unit or to directly accommodate wafers each without a frame unit. The cassette has two side walls, i.e., right and left side walls, provided parallel to each other with a given spacing therebetween. A plurality of right accommodating grooves are formed on the inner surface of the right side wall. The right accommodating grooves are formed at vertical spacings and extend longitudinally and parallel to each other. A plurality of left accommodating grooves are formed on the inner surface of the left side wall in such a manner as to be associated with the right accommodating grooves. The left accommodating grooves are formed at vertical spacings and extend longitudinally and parallel to each other.
According to the experience of the present inventor, however, it has been found that there is a tendency that, during manual placement of a frame unit or wafer into the above conventional accommodation cassette, a specific right accommodating groove and a left accommodating groove one above or below the groove associated with the specific right accommodating groove are erroneously selected. Placing a frame unit or wafer into the cassette with a wrong pair of right and left accommodating grooves may damage the wafer during placement of the frame unit or wafer or result in failure to extract the frame unit or wafer or damage the wafer during automatic extraction of the frame unit or wafer from the accommodation cassette by means of a wafer handling mechanism.
In order to solve the above problem with the conventional accommodation cassette, Japanese Patent Laid-Open No. Hei 7-117810 discloses easy identification of adjacent grooves of each of the right and left accommodating grooves by alternately changing the protrusion lengths or colors of the protruding pieces that define the right and left accommodating grooves on the inner surfaces of the right and left side walls of the accommodation cassette. Further, Japanese Patent Laid-Open No. Hei 9-27543 discloses easy identification of adjacent grooves of each of the right and left accommodating grooves by forming a notch at the front edge portion of every other protruding piece that defines each of the right and left accommodating grooves on the inner surfaces of the right and left side walls of the accommodation cassette.